Thermally conductive gels and encapsulants are soft, compliant and highly conductive materials used to transfer heat away from heat-generating electronic components. It is important that the physical properties of these materials, such as hardness and compliancy, are retained during the life of the electronic component, to protect the electronic devices and maintain good contact with the heat conducting substrates. However, it is often found that with long exposure to temperatures in the 90 to 150° C. range, the hardness of the thermally conductive gels or encapsulants can significantly increase, and the effectiveness of the gels or encapsulants decrease as they begin to fail stay in close contact with the electronic components. Thermally conductive gels and encapsulants have high loading of a thermally-conductive filler in typically an organosiloxane elastomer matrix. Even though the organosiloxane elastomer matrix is stable to temperatures in the 90 to 150° C. range, it is believed that with the filler (and the large amount of surface area from the filler), there are numerous side reactions that can contribute to the increase in hardness over time.
Therefore, there is an unmet need for thermally conductive gels and encapsulants that remain soft and compliant after a prolonged exposure to an elevated temperature.
Phthalocyanine compounds and metal derivatives of these compounds have been used as pigments in silicone resins and in organosiloxane compositions that are subsequently cured to form elastomers either by the use of organic peroxides and heating or by the reaction of hydroxyl-terminated polydiorganosiloxanes with alkyl silicates or organohydrogensiloxanes. References disclosing this use of phthalocyanine compounds include U.S. Pat. No. 3,364,161 British patent no. 1,470,465; and Japanese patent publication nos. 1/279,981 and 62/223,788.
The use of indanthrene blue, terphenyl, phthalocyanines or metal phthalocyanines to impart a resistance to degradation in the presence of heat and ionizing radiation to specified types of silicone elastomers is taught in British patent no. 893,399. The elastomers are cured using an organic peroxide, sulfur or alkyl silicates in the presence of metal salts of carboxylic acids or amines as catalysts. U.S. Pat. No. 2,723,964 teaches using polynuclear benzenoid compounds such as copper phthalocyanine and ingoid dyes to improve the thermal stability of silicone elastomers cured using organic peroxides.
Addition of phthalocyanine to silicone elastomers are known to improve the compression set values of the cured silicone elastomers as taught in U.S. Pat. No. 5,153,244.